GB1056664A - An optical method of and system for transmitting and reading information - Google Patents

Abstract

1,056,664. Electric selective signalling &c. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 10, 1964 [April 12, 1963], No. 14929/64. Headings G4H and G4M. Information is transmitted by means of a light beam to which the information is applied in terms of the angular disposition of a diffraction grating inserted in the beam. Thus if light from a source 31 is collimated by a lens 32 and focused by a lens 33, the introduction of a grating 41 will produce a series of diffracted images lying on a line 42 at right angles to the lines of the grating. If there is introduced into the light beam an object 73, Fig. 7, composed of separate areas P1 ... &c. of differently orientated grat ing, such areas produce diffracted images on radii L1 ... &c., in a plane 75. In Fig. 8 (not shown) the plane 75 is divided into five pairs of sector shaped receiving areas each connected by light-transmitting fibres to one of five light transducers 81-85. The centreal area 79 common to all the diffracted images is blanked out. By insertion of an appropriately oriented diffraction grating in the light beam a signal may be produced on a corresponding transducer in accordance with a quinary code. The signals may be produced, for example, by a film 91, Fig. 9 (not shown), passed through the light beam and having successive areas 92, 93, 94 formed by diffraction gratings differently oriented and separated by opaque areas 95. Such a film may be produced by photographing the image formed by a special cathode-ray tube 201, Fig. 18A (not shown), in the form of a pattern of parallel lines the orientation of which is controlled by a signal from the quinary input 204. In an arrangement as shown in Fig. 7 the object 73 may be imaged in a plane beyond the plane 75, but the image forming rays will pass through the appropriate sectors of the plane 75 corresponding to the orientation of the respective grating forming that part of the object. Thus parts of the object may be displayed in the image plane at will by rotation of a shutter with sector-shaped openings in the plane 75. If the light source is of white light the colour of the selected image may be chosen if shutter apertures of different radial, as well as angular, disposition are employed. In another embodiment a diffraction grating 192 can be rotated by a servo system to a position determined by the voltage applied to it. During the rotation the diffracted light passes through successive pairs of sectors corresponding to those in the plane 75 to fall on a photo-cell generating a voltage. The relationship between the input voltage at the servo terminals and the photo-cell output can be controlled by the choice of the transparency of successive sectors. Fig. 19 shows apparatus for coding a record wherein information is conveyed by the different transparencies of the different areas. The record, at 309, is explored by a flying spot scanner comprising the cathode-ray tube 301 operated by the control device 305. The transparency at any point is indicated by the output of a photo-multiplier tube 302 which is used to produce a pattern of parallel lines on a tube 303, the orientation of the lines being determined by the photomultiplier output. The spot of the tube 303 is positioned by the same control device 305 as that which operates the scanner. By photographing the display on the tube 303 there is obtained a record wherein the different areas of the record shown are rendered as differently orientated diffraction gratings. This record may be reproduced in different colours by apparatus such as already referred to with reference to Fig. 7.